1. Field of the Invention
The present invention relates generally to the field of supply power control.
2. Description of Related Art
Subscriber line (or loop) interface circuitry (SLIC) may be found in or near a central office exchange of a telecommunications network.
One SLIC provides a communications interface between a digital switching network for a central office exchange and an analog subscriber line. The analog subscriber line connects to subscriber equipment, such as a subscriber station or telephonic instrument for example, at a location remote from the central office exchange. The analog subscriber line and subscriber equipment form a subscriber loop.
The SLIC detects and transforms voiceband communications transmitted from the subscriber equipment in the form of low voltage analog signals on the subscriber loop into corresponding digital data for transmission to the digital switching network. For bi-directional communication, the SLIC also transforms digital data received from the digital switching network into corresponding low voltage analog signals for transmission on the subscriber loop to the subscriber equipment.
The SLIC typically uses different power supply levels depending on its operation state. The SLIC may use, for example, one supply level when the subscriber equipment is deactivated or on-hook, another supply level when the subscriber equipment is activated or off-hook, and yet another supply level to signal or ring the subscriber equipment for call progress.
The SLIC may be supplied with power at a fixed or constant supply level sufficient to meet the maximum amount of power to be used by the SLIC. The SLIC, however, would then unnecessarily waste power when the SLIC is in an operation state that uses less power than that supplied to the SLIC. The SLIC would also have to be designed to dissipate a maximum possible amount of wasted power to account for times when the SLIC uses minimum amounts of power.
One SLIC controls a direct-current to direct-current (DC-DC) converter to supply power to the SLIC at different voltage levels. The SLIC may then help reduce or minimize any excess power by helping to control the DC-DC converter to change the voltage supplied to the SLIC as the SLIC changes its power usage. A change in supply voltage from one voltage level to another, however, may cause a current overshoot or surge in the SLIC. For relatively fast and/or larger voltage level changes, an attendant current surge may place a high level of stress on and/or damage one or more circuit components of the SLIC. The SLIC may be designed with components that can better withstand such current surges and/or may be designed with improved current overshoot protection circuitry. Such design considerations, however, may add to the cost, size, and/or complexity of the SLIC.
One SLIC uses a closed-loop pulse width modulation (PWM) converter to control a direct-current to direct-current (DC-DC) converter to supply power to the SLIC at different voltage levels. The SLIC may then help reduce or minimize any excess power by helping to control the DC-DC converter to change the voltage supplied to the SLIC as the SLIC changes its power usage. The PWM converter is designed to operate in accordance with the same controller parameters, such as switching frequency for example, as the PWM converter controls the DC-DC converter to supply power to the SLIC at different voltage levels.